1. Field of the Invention
The present invention relates to the telecommunication field and more in particular to the art of error correction which could be originated during the transmission of signals. Still more in particular, the present invention relates to an improved iterative n-dimensional FEC decoder and an improved method for decoding signals.
This application is based on, and claims the benefit of, European Patent Application No. 04290409.4 filed on Feb. 13, 2004, which is incorporated by reference herein.
2. Description of the Prior Art
As it is known, the Forward Error Correction (FEC) is a technique by means of which redundancy is transmitted together with transported data, using a pre-determined algorithm. The receiving device has the capability of detecting and correcting multiple bit errors that could occur during transmission thanks to the redundancy. The signal transmitted with FEC is more “robust” thus allowing operators to build up longer distance connections without the deployment of many repeater stations.
In other words, in order to overcome transmission errors and packet loss, many telecommunication systems use forward error correction (FEC). In general, FEC schemes transmit extra data which can be used at the receiving end to re-create any corrupted or lost packets. For instance, FEC has been applied to CD-ROMs to compensate for scratches, and used in satellite and deep-space transmissions, since the broadcast is in only one direction (i.e. the receiver is incapable of asking for retransmission).
A known method for performing a decoding of an n-dimensional code consists in decoding first along a first dimension, then along a second dimension, then along a third dimension up to the nth dimension. Moreover, in order to improve the error correction capability, it is possible to carry out a number of iterations similar to the above mentioned one (namely, decoding in a 1st, 2nd, 3rd, . . . nth dimension). Each iteration results in a delay or latency.
In turn, the step of decoding in one dimension comprises: calculating syndromes, calculating error positions and error values; and finally performing correction in that dimension.
These operations are iterated along the n dimensions.
The processing of calculated syndromes allows establishing how many errors are present and where they are located.
In other words, the computed syndromes provide information from which the error positions and their value can be derived.
The error position calculation step is generally carried out by verifying an equation at all the possible points (positions, CHIEN search). A better alternative consists in making a calculation in a closed form.
The known solution results in two main disadvantages. The first disadvantage is a high latency that depends on the number of iterations that are performed for correcting errors. To increase the error correctability, as said above, it is necessary to carry out a number of iterations, each single iteration resulting in a latency. This implies that, in order to raise the net coding gain of a decoder, it is necessary to increase the number of iterations and then the latency. The second disadvantage is given by the complexity of the decoder. In fact, it is requested to re-compute all the syndromes at each decoding step which is considered as a single sub-iteration independent from the others.